Previous i am using Xcode 6.4 or below, In that I didn't notify this type issues. but now I am getting noticeable problems in Xcode 7.2 in related CGRectMake x,y Position.
CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat screenWidth = screenRect.size.width;
CGFloat screenHeight = screenRect.size.height;
UIView *smallView=[[UIView alloc]initWithFrame:CGRectMake(screenWidth/2, screenHeight/2, 100, 100)];
smallView.backgroundColor=[UIColor redColor];
[self.view addSubview:smallView];
NSLog(@"%f",smallView.frame.origin.x);// 137.500000
above snip code, the position of x & y not perfect. the below image is output . 
but if i add center=self.view.ceter It will come to center. the output is 
smallView.center=self.view.center;
the problem is , in both case x & y position values same ,
NSLog(@"%fn%fn%ff%f ",screenWidth/2,screenHeight/2,self.view.center.x,self.view.center.y);
Why they will show different result, how can i do without using center property. or Shall go for Autolayout .